When a California woman asked surgeons to sever the lines of communication between the halves of her brain, she just hoped for some relief from uncontrollable epileptic seizures.
The surgery helped. It has also given researchers surprising new information about the unusual way that this left-handed woman's brain manages speaking and writing -- information that could be useful in studying the evolution of human speech and written language.
The story of the woman called V.J., first told at a science conference in 1996 by UC Davis neuroscientist Kathleen Baynes, is described in new detail by Baynes and colleagues in the Friday, May 8, issue of the journal Science.
In this study, the post-surgery abilities of two other split-brain cases are compared to V.J.'s. Those patients are right-handed. Each is able to write words displayed to the left side of the brain, but not words displayed to the right. That makes sense, since the left side of the brain controls speaking, reading and writing in most people.
V.J. is different. She can write words displayed to the right side of her brain, but not words displayed to the left.
After hundreds of hours of tests, Baynes and her colleagues have concluded that the left side of V.J.'s brain controls reading aloud and speaking, while writing is controlled by the right side.
"This is the first direct evidence that the right hemisphere might control writing in left-handed people," Baynes says. The findings also support the idea that spoken and written language evolved independently, she says, because "they're not inherently linked."
Materials provided by University Of California, Davis. Note: Content may be edited for style and length.
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